U.S. patent application number 11/973671 was filed with the patent office on 2009-03-26 for immersion lithography laser light source with pulse stretcher.
This patent application is currently assigned to Cymer, Inc.. Invention is credited to Edward Arriola, Robert A. Bergstedt, Daniel J.W. Brown, Walter Crosby, Ed Danielewicz, Alexander I. Ershov, John Fitzgerald, Vladimir B. Fleurov, Igor V. Fomenkov, Robert N. Jacques, William N. Partlo, Rajasekhar M. Rao, German Rylov, Richard L. Sandstrom, Robin Swain, Christian J. Wittak, Mike Wyatt.
Application Number | 20090080476 11/973671 |
Document ID | / |
Family ID | 40471523 |
Filed Date | 2009-03-26 |
United States Patent
Application |
20090080476 |
Kind Code |
A1 |
Partlo; William N. ; et
al. |
March 26, 2009 |
Immersion lithography laser light source with pulse stretcher
Abstract
An apparatus and method which may comprise a pulsed gas
discharge laser which may comprise a seed laser portion; an
amplifier portion receiving the seed laser output and amplifying
the optical intensity of each seed pulse; a pulse stretcher which
may comprise: a first beam splitter operatively connected with the
first delay path and a second pulse stretcher operatively connected
with the second delay path; a first optical delay path tower
containing the first beam splitter; a second optical delay path
tower containing the second beam splitter; one of the first and
second optical delay paths may comprise: a plurality of mirrors
defining the respective optical delay path including mirrors
located in the first tower and in the second tower; the other of
the first and second optical delay paths may comprise: a plurality
of mirrors defining the respective optical delay path including
mirrors only in one of the first tower and the second tower.
Inventors: |
Partlo; William N.; (Poway,
CA) ; Ershov; Alexander I.; (San Diego, CA) ;
Rylov; German; (Poway, CA) ; Fomenkov; Igor V.;
(San Diego, CA) ; Brown; Daniel J.W.; (San Diego,
CA) ; Wittak; Christian J.; (San Diego, CA) ;
Rao; Rajasekhar M.; (San Diego, CA) ; Bergstedt;
Robert A.; (Carlsbad, CA) ; Fitzgerald; John;
(San Diego, CA) ; Sandstrom; Richard L.;
(Encinitas, CA) ; Fleurov; Vladimir B.;
(Escondido, CA) ; Jacques; Robert N.; (San Diego,
CA) ; Danielewicz; Ed; (Carlsbad, CA) ; Swain;
Robin; (Trabuco Canyon, CA) ; Arriola; Edward;
(Huntington Beach, CA) ; Wyatt; Mike; (Santa
Margarita, CA) ; Crosby; Walter; (Los Alamitos,
CA) |
Correspondence
Address: |
William C. Cray;Cymer, Inc.
Legal Dept., 17075 Thornmint Court, MS/4-2D
San Diego
CA
92127-2413
US
|
Assignee: |
Cymer, Inc.
San Diego
CA
|
Family ID: |
40471523 |
Appl. No.: |
11/973671 |
Filed: |
October 10, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60994497 |
Sep 20, 2007 |
|
|
|
Current U.S.
Class: |
372/25 ;
372/94 |
Current CPC
Class: |
G03F 7/70583 20130101;
H01S 3/0057 20130101; G03F 7/70341 20130101 |
Class at
Publication: |
372/25 ;
372/94 |
International
Class: |
H01S 3/139 20060101
H01S003/139; H01S 3/083 20060101 H01S003/083 |
Claims
1. An apparatus comprising: a pulsed gas discharge laser
lithography light source comprising: a seed laser portion providing
a seed laser output light beam of seed pulses; an amplifier portion
receiving the seed laser output light beam and amplifying the
optical intensity of each seed pulse to provide a high power laser
system output light beam of output pulses; a pulse stretcher
increasing the number of peaks in the output pulse and decreasing
the average peak intensity of each of the output pulses by passing
the output pulses through a pair of optical delay paths in series;
the pulse stretcher comprising: a first beam splitter operatively
connected with the first delay path and a second pulse stretcher
operatively connected with the second delay path; a first optical
delay path tower containing the first beam splitter; a second
optical delay path tower containing the second beam splitter; one
of the first and second optical delay paths comprising: a plurality
of mirrors defining the respective optical delay path including
mirrors located in the first tower and in the second tower; the
other of the first and second optical delay paths comprising: a
plurality of mirrors defining the respective optical delay path
including mirrors only in one of the first tower and the second
tower.
2. The apparatus of claim 1 further comprising: the first optical
delay path and the second optical delay path being of unequal
length.
3. The apparatus of claim 1 further comprising: the first optical
delay path being longer than the second optical delay path.
4. The apparatus of claim 2 further comprising: the one of the
first and second optical delay towers containing mirrors in both of
the first and second towers being the longer of the first and
second optical delay paths.
5. The apparatus of claim 3 further comprising: the one of the
first and second optical delay towers containing mirrors in both of
the first and second towers being the longer of the first and
second optical delay paths.
6. The apparatus of claim 4 further comprising: the longer of the
first and second optical delay paths being the first optical delay
path.
7. The apparatus of claim 1 further comprising: the mirrors
comprising imaging mirrors.
8. The apparatus of claim 6 further comprising: the mirrors
comprising imaging mirrors.
9. The apparatus of claim 1 further comprising: the mirrors
comprising confocal mirrors.
10. The apparatus of claim 6 further comprising: the mirrors
comprising confocal mirrors.
11. The apparatus of claim 8 further comprising: the mirrors
comprising confocal mirrors.
12. An apparatus comprising: a pulsed gas discharge laser
lithography light source comprising: a seed laser portion providing
a seed laser output light beam of seed pulses; an amplifier portion
receiving the seed laser output light beam and amplifying the
optical intensity of each seed pulse to provide a high power laser
system output light beam of output pulses; the amplifier portion
comprising a ring power amplifier comprising amplifier portion
injection optics comprising at least one beam expanding prism, a
beam reverser and an input/output coupler; the beam expansion
optics and the output coupler being mounted on an optics assembly
with the beam expansion optics rigidly mounted with respect to the
optics assembly and the input/output coupler mounted for relative
movement with respect to the optics assembly for optical alignment
purposes.
13. The apparatus of claim 12 further comprising: the input/output
coupler being mounted for movement with respect to the optic
assembly in a first axis and a second axis.
14. The apparatus of claim 13 further comprising: the first axis
and second axis being generally orthogonal to each other.
15. The apparatus of claim 12 further comprising: the amplifier
injection optics being contained within an amplifier portion
injection optics assembly box and the input/output coupler
comprising at least one through-the-wall adjusting actuator to
adjust the position of the input/output coupler in at least one
axis.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Patent
Application Ser. No. 60/994,497, filed Sep. 20, 2007. The present
application is related to U.S. patent application Ser. No.
11/787,180 filed on Apr. 13, 2007, entitled LASER SYSTEM, Attorney
Docket No. 2006-0083-04, and to U.S. patent application Ser. No.
11/805,583, entitled HIGH POWER EXCIMER LASER WITH A PULSE
STRETCHER, filed on May 23, 2007, Attorney Docket No. 2006-0040-02,
the disclosures of each of which are incorporated herein by
reference.
FIELD
[0002] The present disclosed subject matter relates to, laser
produced light sources, such as DUV or EUV light sources, such as
are used for integrated circuit photolithography manufacturing
processes or irradiation processing applications such as elongated
beam annealing processes for, e.g., thin film transistor panel
production or laser produced plasma EUV light generation, and more
specifically to pulse stretching for such laser systems to increase
the T.sub.is and/or reduce coherence or the like.
BACKGROUND
[0003] Pulse stretching has been known in the past for high power
pulsed DUV lasers such as are used for integrated circuit
manufacturing photolithography processes as a photoresist exposure
light source, as is shown, e.g., in the above referenced co-pending
Ser. No. 11/805,583 patent application. With increasing pulse
energy requirements to meet higher average power requirements,
e.g., for new immersion lithography processes used to extend the
DUV wavelength light source scanner capabilities to smaller CD
nodes, there has developed a need for improved pulse stretching,
which at the same time for economic and other reasons there is a
need to keep the pulse stretcher in essentially the same footprint
as in earlier laser light source systems. According to aspects of
embodiments of the disclosed subject matter applicants propose a
solution to this dilemma. Similarly Applicants' assignee has chosen
to utilize a power amplification stage such as is disclosed in the
above referenced co-pending Ser. No. 11/787,180 patent application.
Certain optical considerations such as complex alignment issues
have led applicants to propose, according to aspects of embodiments
of the disclosed subject matter to solutions to problems arising
from those considerations.
SUMMARY
[0004] An apparatus and method are disclosed which may comprise a
pulsed gas discharge laser lithography light source which may
comprise a seed laser portion providing a seed laser output light
beam of seed pulses; an amplifier portion receiving the seed laser
output light beam and amplifying the optical intensity of each seed
pulse to provide a high power laser system output light beam of
output pulses; a pulse stretcher increasing the number of peaks in
the output pulse and decreasing the average peak intensity of each
of the output pulses by passing the output pulses through a pair of
optical delay paths in series; the pulse stretcher may comprise: a
first beam splitter operatively connected with the first delay path
and a second pulse stretcher operatively connected with the second
delay path; a first optical delay path tower containing the first
beam splitter; a second optical delay path tower containing the
second beam splitter; one of the first and second optical delay
paths may comprise: a plurality of mirrors defining the respective
optical delay path including mirrors located in the first tower and
in the second tower; the other of the first and second optical
delay paths may comprise: a plurality of mirrors defining the
respective optical delay path including mirrors only in one of the
first tower and the second tower. The first optical delay path and
the second optical delay path may be of unequal length. The first
optical delay path may be longer than the second optical delay
path. The other of the first and second optical delay towers
containing mirrors in both of the first and second towers may be
the longer of the first and second optical delay paths. The longer
of the first and second optical delay paths may be the first
optical delay path in the series arrangement. The mirrors may
comprise imaging mirrors in a confocal or non-confocal
arrangement.
[0005] An apparatus and method are disclosed which may comprise a
pulsed gas discharge laser lithography light source which may
comprise a seed laser portion providing a seed laser output light
beam of seed pulses; an amplifier portion receiving the seed laser
output light beam and amplifying the optical intensity of each seed
pulse to provide a high power laser system output light beam of
output pulses; the amplifier portion may comprise a ring power
amplifier comprising amplifier portion injection optics comprising
at least one beam expanding prism, a beam reverser and an
input/output coupler; the beam expansion optics and the output
coupler may be mounted on an optics assembly with the beam
expansion optics rigidly mounted with respect to the optics
assembly and the input/output coupler mounted for relative movement
with respect to the optics assembly for optical alignment purposes.
The input/output coupler may be mounted for movement with respect
to the optic assembly in a first axis and a second axis. The first
axis and second axis may be generally orthogonal to each other. The
amplifier injection optics may be contained within an amplifier
portion injection optics assembly box and the input/output coupler
may comprise at least one through-the-wall adjusting actuator to
adjust the position of the input/output coupler in at least one
axis.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 shows schematically and in block diagram form a high
poser lithography laser light source according to aspects of an
embodiment of the disclosed subject matter;
[0007] FIG. 2 shows a perspective view of mirror mounts forming a
pair of optical delay path towers according to aspects of an
embodiment of the disclosed subject matter;
[0008] FIGS. 3A and 3B illustrate partly schematically optical
delay paths with one delay path sharing tower mirror mounts with
the tower of the other delay path according to aspects of an
embodiment of the disclosed subject matter;
[0009] FIG. 4 shows a perspective view of an opened end box
containing mirror mounts from a pair of delay path mirror towers
forming part of an optical path enclosure according to aspects of
an embodiment of the disclosed subject matter;
[0010] FIGS. 5A and 5B illustrate the effect of pulse stretching in
a first delay path followed by a second delay path in series
according to aspects of an embodiment of the disclosed subject
matter;
[0011] FIG. 6 shows a partly exploded perspective view of a seed
laser injection system enclosure box according to aspects of an
embodiment of the disclosed subject matter;
[0012] FIGS. 7A, 7B, 7C and 7D show, respectively an exploded
perspective view, a bottom plan view, a cross sectional view and a
detailed view of a seed laser injection system enclosure box top
and its contents according to aspects of an embodiment of the
disclosed subject matter;
[0013] FIGS. 8A, 8B and 8C show, respectively an first and second
exploded perspective view and a cut-away portion of an exploded
perspective view of a seed laser injection system enclosure box
bottom and its contents according to aspects of an embodiment of
the disclosed subject matter;
[0014] FIGS. 9A, 9B, 9C and 9D show, respectively, a top plan view,
a first and a second cross-sectional view and a detail view of a
seed laser injection system enclosure box bottom and its contents
according to aspects of an embodiment of the disclosed subject
matter;
[0015] FIGS. 10A, 10B, 10C and 10D show, respectively a first
second and third partly exploded perspective view and a detailed
view of an optics assembly according to aspects of an embodiment of
the disclosed subject matter.
DETAILED DESCRIPTION OF THE DISCLOSED SUBJECT MATTER
[0016] According to aspects of an embodiment of the disclosed
subject matter a very high power, e.g., 90 W or better very high
pulse repetition rate, e.g., upwards of 6 kHz and above, gas
discharge laser system 10, as shown illustratively and in block
diagram for in FIG. 1 can be provided with a simple and compact
pulse stretcher, which applicants' assignee refers to as an Optical
Pulse Stretcher ("OPuS") 62, which may be defined by certain
required optical and mechanical performance specifications. Table I
indicates abbreviations, terms and acronyms that may be used in the
description of aspects of embodiments of the disclosed subject
matter.
TABLE-US-00001 TABLE I Term/ Acronym Definition AS Autoshutter BAM
Bandwidth Analysis Module. Measures bandwidth and pulse energy. BR
Beam Reverser - Refers to the module that redirects the beam for
the second pass through the PRA chamber FWHM Full Width at Half
Maximum. A common measure of pulse width. HR High Reflector IMS
Interlock Management System IRM Imaging Relay Mirrors LAM Line
center Analysis Module. Measures wavelength and pulse energy. LNM
Line Narrowing Module. MO Master Oscillator. The laser resonator in
a MOPRA system. It generates pulses with the necessary spectral
properties but insufficient pulse energy. MOPRA Master
Oscillator-Power Ring Amplifier. The two-chamber laser
architecture. OC Output Coupler. OPuS Optical Pulse Stretcher. 4x
OPuS A version of an OPuS that combines two pulse stretchers in
series to achieve a T.sub.IS magnification of 4 PRA Power Ring
Amplifier. The second chamber in a MOPRA system. When the pulses
from the MO pass through the gain medium of the PRA, the necessary
pulse energy is obtained for the ultimate laser system output.
T.sub.IS Time Integral Squared TWA Through the Wall Adjuster WEB
Wavefront Engineering Box. Refers to the modules that steer the
beam from the MO to the PRA.
[0017] Turning now to FIG. 1 there is illustrated a gas discharge
laser system 10, which may include, e.g., a solid state or gas
discharge seed laser system 12, illustrated as a relatively broad
band gas discharge seed system 12, an amplification stage, e.g., a
power ring amplifier ("PRA") stage 14, such as is discussed in more
detail in the U.S. application Ser. No. 11/787,180 referenced
above, relay optics 16 and laser system output optics 20. The seed
system may include, e.g., a seed laser chamber 30, in which, e.g.,
electrical discharges between electrodes (not shown) may cause
lasing gas discharges in a lasing gas to create an inverted
population of high energy molecules, e.g., including Ar, Kr, Xe or
CO.sub.2 to produce relatively broad band radiation which may be
line narrowed to a relatively very narrow bandwidth and center
wavelength selected in a line narrowing module (LNM") 32, as is
known in the art. The seed laser system 12 may also include an
output coupler 34, which may comprise a partially reflective
mirror, forming with a reflective grating (not shown) in the LNM
32, an oscillator cavity in which the seed laser 12 oscillates to
form the seed laser output pulse, i.e., forming a master oscillator
("MO"). A MO wavefront engineering box ("WEB") 38 may serve to
redierect the output of the MO seed laser system 12 toward the
amplification stage 14, and may include, e.g., beam expansion with,
e.g., a multi prism beam expander (not shown) and coherence
busting, e.g., in the form of an optical delay path (not shown) as
is also discussed in more detail in the U.S. application Ser. No.
11/787,180 referenced above.
[0018] The amplification stage 14 may include, e.g., a lasing
chamber 50, which may also be an oscillator, e.g., formed by seed
beam injection and output coupling optics (not shown) which may be
incorporated into a PRA wavefront engineering box ("WEB") 52 and
may be redirected back through the gain medium in the chamber 50 by
a beam reverser 54. The PRA WEB 52 may incorporate a partially
reflective input/output coupler (not shown) and a maximally
reflective mirror for the nominal operating wavelength (e.g., at
around 193 nm for an ArF system) and beam expansion prisms as are
more fully described in the just referenced U.S. application.
[0019] A bandwidth analysis module ("BAM") 60 at the output of the
amplification stage 14 may receive the output laser light beam of
pulses from the amplification stage and pick off a small portion
for metrology purposes, e.g., to measure the output bandwidth and
pulse energy. The laser output light beam of pulses then passes
through an OPuS 62, discussed in more detail below and an output
auto shutter 64, which may also be the location of a pulse energy
meter in lieu of in the BAM 60.
[0020] The OPuS module 62 may be mounted vertically between a laser
system Bandwidth Analysis Module ("BAM") 60 at the output of the
laser amplifier portion 14 and the autoshutter 64, forming the
output of the laser system 10 itself. The purpose of the OPuS 62
may be, e.g., to convert a single output laser pulse, e.g., as
illustrated in FIG. 5A, into a pulse train, e.g., as illustrated in
FIGS. 5A and 5B together. Each one of the secondary pulses, e.g.,
204, 206, 208 and 210 in FIG. 5A and 232, 234, 236, 238 and 240 in
FIG. 5B, e.g., created from the original pulse 200 shown
illustratively in FIG. 5A, e.g., may be delayed with respect to
each other in time. By distributing the original laser pulse energy
into a train of secondary pulses, the effective pulse length of the
laser can be expanded and at the same time the peak pulse intensity
reduced. The OPuS module 62 can thus receive the laser beam from
the PRA WEB 60 and direct the output of the OPuS 62 to the
autoshutter 64. FIG. 5 A shows illustratively the effect of a 22 ns
delay path with 97% reflective mirrors and a 60% reflective beam
splitter (with an 8% loss) and an input pulse (from the laser)
T.sub.is of 20.78 ns resulting in a 53.97 ns T.sub.is output and
FIG. 5B illustrates by way of example putting that pulse through a
second 18 ns delay path using 97% reflectivity mirrors with a 60%
reflective beam splitter (8% loss), resulting in an 81.9 ns. Such
an OPuS is exemplary of state of the art pulse stretchers of this
kind and needs to be improved to about 100 ns T.sub.is, e.g., by,
according to aspects of an embodiment of the disclosed subject
matter increasing the first delay path to about 42 ns while
maintaining essentially the same footprint (e.g., same enclosure
available space in the laser system frame)
[0021] The function of the OPuS module 62 is to, e.g., increase the
output pulse length of the laser beam produced by the PRA 14. If
unmodified the short pulse length, e.g., illustrated as pulse 200
in FIG. 5A, together with the high energy and DUV wavelength of the
output beam from the PRA 14, can, e.g., damage the optics of, e.g.,
a photolithography system using for manufacturing integrated
circuits, and receiving the output laser light, for which the laser
system 10 is designed, as is discussed in some further detail in
the U.S. application Ser. No. 11/787,180 referenced above. This
damage can take on several forms, e.g., photon induced absorption
and photon induced index variation. The index variation damage
mechanism can be subdivided into several categories, e.g.,
compaction and de-compaction. At this time, however, only
compaction has been determined to be dependent upon pulse length.
Compaction is a process of densification, which causes, e.g., a
change in the index of refraction. The amount of compaction has
been found to be inversely proportional to the pulse width of the
incident beam. Thus the higher the time integrated squared function
of the laser output light pulse ("T.sub.is") the better.
[0022] According to calculations that have been done, one can
expect that the maximum T.sub.IS magnification of a pulse
stretcher, such as is described in more detail below, for an input
pulse with a T.sub.IS of 19 nsec is about 2.75, with an efficiency
of about 86%. Another notable item of interest is the sensitivity
of the T.sub.IS magnification to beam splitter (a part of the
described OPuS pulse stretcher 62) reflectivity. Variations in beam
splitter reflectivity can have a significantly higher effect on
T.sub.IS magnification than output efficiency. Thus, the output
pulse length could be well below specification while the output
efficiency could be little changed. In addition to beam splitter
reflectivity, the reflectivity of the imaging relay mirrors "IRM",
e.g., as illustrated in FIGS. 3A and 3B also have a significant
impact on T.sub.IS magnification. However, unlike the beam
splitter(s), the reflectivity of the IRMs have a significant impact
on the output efficiency. Input pulse length also influences
T.sub.IS magnification. The T.sub.IS metric for measuring pulse
length is maximized when each of the sub-pulses are completely
separated in time. Since the delay length of the pulse stretcher,
e.g., OPuS 62, is fixed, its T.sub.IS magnification capability can,
e.g., be continually diminished as the input pulse length becomes
increasingly longer than its fixed delay length. The input pulse
length, however, has no effect on the output efficiency of the
pulse stretcher.
[0023] According to aspects of an embodiment of the disclosed
subject matter, the physical size of the pulse stretcher can be
directly related to the output pulse width size from the PRA 14 and
the pulse width size specified for the output of the laser system
10. The design can be based on the assumption that the output pulse
width of the PRA 14 has a T.sub.IS of 40 nsec and the required
output T.sub.IS of the laser system 10 is 115 nsec. The OPUS module
62 may then occupy an envelope of dimensions given by a length of
1750 mm, a width of 125 mm, and height of 250 mm and accommodate a
12 mm.times.12 mm to 15 mm.times.15 mm size laser beam.
[0024] Another factor that influences T.sub.IS magnification can be
polarization. The beam splitter, e.g., for the input into each
delay path 150, 190, may be coated to obtain a specific
reflectivity for a given polarization. If the polarization is
different than that for which the coating is designed, the
polarization variance can have the effect of changing the
reflectivity of the beam splitter. The beam splitter's reflectivity
change can, in turn, change the T.sub.IS magnification, as
previously noted. Polarization effects of the OPUS 62 are also not
limited to T.sub.IS magnification. The OPuS 62 beam splitter(s) can
change the polarization state of the input beam polarization. These
effects may be most evident, e.g., when the beam splitter is
subjected to a high power load. At high power the beam splitter may
be thermally stressed, e.g., by its finite absorption. This thermal
stress may, in turn, increase the magnitude of the intrinsic
birefringence of the beam splitter. The beam splitters of the first
delay path 150 and second delay path 190 of the OPUS 62 may be
particularly sensitive to small amounts of birefringence since the
beam may refract through the optic up to as many as six times and
each pass through the beam splitter has a cumulative effect on the
polarization. This power induced birefringence of the beam splitter
manifests itself as a degradation of the output laser polarization
purity, particularly for the beam splitter in the first delay path
150.
[0025] To mitigate the effects of power induced birefringence, the
beam splitter optic(s) can be rotated or clocked to find an
orientation that has a birefringence null. This can involve
illuminating a test sample with a highly polarized beam and
observing the polarization changes of the beam after it has been
transmitted by the sample. In addition to clocking, the power
induced birefringence can be reduced by minimizing the amount of
absorption of the beam splitter. It has been found that the most
significant contributor to absorption is the beam splitter coating.
If the coating materials are chosen to minimize absorption, the
thermal stress on the optic can be reduced.
[0026] If the T.sub.IS magnification needs to be increased beyond
what is capable from a single pulse stretcher, two pulse stretchers
can be connected in series. This may be explained by the fact that
a single pulse stretcher can only produce a finite amount of
secondary pulses with significant amplitude defined as those with
amplitude greater than from about 1% to 5% of that of the input
pulse. The amount of significant secondary pulses produced from the
original input pulse can be effectively squared in a dual pulse
stretcher design.
[0027] Unfortunately, according to certain applications of aspects
of an embodiment of the disclosed subject matter a maximum output
pulse length from a second pulse stretcher delay path, e.g., 190,
may not be 2.75 times the output pulse length of the first pulse
stretcher delay path 150. The reason is that in order for the
second pulse stretcher to obtain the same pulse length
magnification as the first it should have an optical delay equal to
the pulse length of its input. If the first pulse stretcher delay
path, e.g., 150, expands the pulse length to 55 nsec, the second
pulse stretcher delay path, e.g., 190, could require a delay of 55
nsec. This could require a physical length of 413 cm (4130 mm). If
the second pulse stretcher delay path 190 is, e.g., constrained to
have a delay length equal to or shorter than the first pulse
stretcher delay path 150, than each of the output pulses can be
overlapped in time which can, e.g., reduce the maximum pulse length
expansion capability from the maximum value of 2.75.
[0028] Additionally, if the optical delay path, e.g., 150 and 190
of each of the pulse stretchers, e.g., in a two delay path OPuS 62,
is different, a greater increase in the output pulse length can be
obtained than two pulse stretchers with the same optical delay.
This is a result of the non-uniform, temporal distribution of the
input pulse. Having the second pulse stretcher with a different
optical delay than the first can creates an additional degree of
freedom of changing the temporal location of the pulse train output
of the second pulse stretcher delay path 190 with respect to the
pulse train output of the first pulse stretcher delay path 150.
This can create the possibility of designing the optical delay of
the second pulse stretcher delay path 190 to fill in the holes
(areas of low amplitude) of the pulse train produced by the first
pulse stretcher delay path 150.
[0029] According to aspects of an embodiment of the disclosed
subject matter the OPuS module 62 may incorporate a plurality of,
e.g., three base plates 92A, 92B and 90. Two of the baseplates, 92A
and 92B may, e.g., mount each of a pair of IRM mirror mounts 98A
for the longer first delay path 150 and 98B for the shorter second
delay path 190. The third baseplate 90 may attach the beam splitter
mount 80. The baseplates 82A, 82B and 90 may be made of stainless
steel to match the material of the vertical optics table (not
shown). Having the baseplates 92A, 92B and 90 separable from the
enclosure(s) of the modules can enable extension of the surface of
the optics table so that the optics mounts can mount directly to
it. The stability and rigidity of the vertical optics table can
provide an accurate mounting surface for the optics. In addition,
however, due to the difficulty in precision cleaning the vertical
table, the base plates 92A, 92B and 90 may be used to provide a
clean extension of the vertical table.
[0030] Individual covers similar to that shown as 82B in FIG. 4 may
be used in the OPuS module 62. The covers may be used, e.g., to
enclose the mirror mounts 98A and 98B, e.g., shown in FIG. 4,
having a housing 110 including a housing wall 112, and abeam
passage opening 114, and the middle box 122 of the OPuS enclosure,
which may house the beam splitter mounts 84 and beam passage
opening 86, between a rear wall 88 and a stanchion 89. Two end
boxes, as shown in more detail in the above referenced co-pending
Ser. No. 11/805,583 patent application may contain both features
for through-the-wall adjusters ("TWA's") and view ports. TWA's may
provide a sealed mechanical feed through to certain IRM adjustments
and the alignment shutter that may be meant to be adjustable
without breaking the enclosure. The view port feature of the cover
boxes, e.g., the end boxes, may provide a quick alignment
diagnostic capability. They may, e.g., provide a view of the beam
footprint on a respective IRM without the need for removing the
respective end box covers. The covers may also provide service
access ports for field replaceable optical subassemblies and
components. Also, the covers may be made of aluminum and can be
exposed to the nitrogen purged volume they may need to be nickel
plated, e.g., with electroless nickel plating. An enclosure 130 for
the OPuS 62 may be, e.g., an aluminum weldment, which may have
flanges on both sides to attach to and seal with both the
baseplates 90, 92A, 92B and the covers. The enclosure may also need
to be nickel plated.
[0031] Each of the imaging relay mirror mounts 98A and 98B may
contain three IRMs, e.g., in the openings 100 shown in FIG. 2. The
mounts 98A and 98B may be designed to allow for at least one of the
mirrors to be adjustable, e.g., via a TWA's while other mirrors may
have an adjustment accessible from only inside the module
enclosure. The TWA adjustments may be accessed through the covers
120a, 120B, e.g., via a sealed mechanical feed-through. The IRM
optical mounts 98A, 98B may also be nickel plated. A beam splitter
mount 80 may contain the beam splitter optic or optics (not shown)
held in the beam splitter mounting plates 84A (for the first delay
path 150) and 84B (for the second delay path 190). The mount 80 may
also provide the attachment surface for the system aperture. The
mount 80 may have no adjustments for the beam splitter mirrors (not
shown) held in the respective mounting plate 84A, 84B, and may also
be a field replaceable unit. The mount 80 may also be nickel
plated. A system aperture will be attached to the beam splitter
mount and will be located after the beam splitter optic(s) held in
the respective one of the mounting plates 84A and 84B. The aperture
size may be 12.times.12 mm and may be used to provide the point of
reference for measuring the laser system beam parameters.
[0032] Turning now to FIGS. 3A and 3B there is illustrated
schematically and not to scale a perspective view of the optics in
an OPuS module 62, which may comprise, e.g., a first delay path 150
and a second delay path for an Opus module 62 according to aspects
of an embodiment of the disclosed subject matter. In the first
delay path an input laser light beam 140 of pulses, e.g., output
from the BAM 60 may enter the delay path 150, e.g., by being split
in a partially reflective beam splitter mirror. to form, e.g., an
output beam 142 of laser pulses from the first delay path 150 and a
first delay path 152 from the beam splitter (not shown) to the
first imaging relay mirror 154, which sends a beam along a second
path 156 to the second imaging relay mirror 158, which in turn
reflects a beam 160 to a third mirror 162, from which mirror 162 is
reflected a beam along a fourth path 164, which may, e.g.,
intersect the beam 156 at a focal point of the mirrors 154 and 162,
to a fourth imaging relay mirror 168, which may, in turn reflect
the beam of laser pulses along a fifth path 170 to a fifth imaging
relay mirror 172, which in turn may reflect the beam along a sixth
path 174 to a sixth imaging relay mirror 176, and thence also along
a seventh delay path 178, crossing the beam 170 at a focal point of
the mirrors 170 and 176, to a seventh imaging relay mirror 180, and
further along an eighth delay path 182 to the final eighth mirror
184 of the delay path 150, from which the beam is reflected along a
ninth path 186 back to the beam splitter (not shown) for delay path
150. A wedge or like alignment optic may be, e.g., in the ninth
delay path to align the portion of the beam along path 186 with the
portion of the beam 142 that initially was not reflected by the
beam splitter at the entry to delay path 150.
[0033] The beam 142 may form the input for a second OPuS delay path
190, which may be a partially reflective mirror that transmits an
output beam 144 and a beam traveling along a first delay path 192
of the optical delay 190 to a first imaging relay mirror 194, from
which is reflected a beam along a second delay path 193, to a
second imaging relay mirror 195, and thence to a third path 196 to
a third imaging relay mirror 198, followed by a fourth path 200 and
a fourth imaging relay mirror 202, followed by a fifth path 204
returning back to the beam splitter (not shown) for the second
delay path 190, which may also include an aligning wedge to align
the output of the beam splitter resulting from the incidence of the
beam along delay path 204 with the transmitted portion of the beam
142 received from the output of the first delay path 150 and the
portion of the original laser input beam 140 transmitted by the
first delay path beam splitter (not shown) and, therefore, not
input into thee first optical delay path 150.
[0034] It will be noted that the mirrors 172 and 176 in the first
delay path 150 may be housed in the mirror mounts 98B (as shown in
FIG. 2 for the second delay path Turning to FIGS. 5A and 5B there
is illustrated by way of example two graphs depicting an example of
a maximum output pulse length produced from two pulse stretchers
delay paths, e.g., 150 and 190, connected in series with the path
length constraint that, e.g., the maximum optical delay of a single
pulse stretcher is 22 nsec. The reflectivity of the IRMs was
assumed to be greater than 97% and the loss at the beam splitter is
assumed to be 8% per pass. If the input pulse T.sub.IS is 20.8 nsec
and the delay length of the first pulse stretcher is 22 nsec, the
output pulse T.sub.IS from the first pulse stretcher will be
approximately 54 nsec[, incorporating peaks 204, 206, 208, and 210
of FIGS. 5A and 5B.]. If the output from the first pulse stretcher
is then input to a second pulse stretcher, e.g., with a delay of 18
nsec, the final output pulse T.sub.IS will be approximately 82
nsec, incorporating peaks 323, 324, 236, 238, and 240 in FIG. 5B.].
Although the pulse length expansion of two pulse stretchers in
series may not simply multiply, the output efficiency may multiply.
Therefore, if the reflectivity of the imaging relay mirrors is
estimated to be 97% and the absorption and reflection losses for
each pass through the beam splitter is 2%, then the expected output
efficiency of two pulse stretchers in series would be (0.85)(0.85)
or about 70%.
[0035] The OPuS module 62 may be composed of the following internal
components. A beam splitter mount 80 and optics which may serve to,
e.g., direct a percentage of the incident beam (output laser beam
of pulses from the PRA 14) to the IRMs forming a first delay path
150 (FIGS. 3A and 3B) while transmitting the rest of the output
beam of pulses from the laser system 10, e.g., to a second pulse
stretcher delay path 190. The first beam splitter (not shown in
FIG. 3A or FIG. 3B) in the OPuS module 62 can have a predetermined
reflectivity and transmission. However, the exact values of
transmission and reflection may be dependent upon the optical
configuration of the OPuS module 62. Imaging relay mirrors, e.g.,
154, 158, 162, 168, 172, 176 and 180 of the first delay path 150
illustrated schematically in FIGS. 3A and 3B, may be mounted on a
pair of imaging mirror mounts 82A and 82 B (FIG. 2). The IRMs may
preserve the spatial and divergence properties of the input beam
140 while, e.g., also propagating it through a first delay path 150
before it is recombined with the original incident beam 140 to
form, e.g., the input beam 142 for a second OPuS module 62 delay
path 190. The IRMs may be spherical concave mirrors, e.g., also
coated for maximum reflection at normal incidence for a given
nominal wavelength. A system aperture (not shown) may be attached
to the beam splitter mount 80 after the beam splitter optic (not
shown). This aperture may be used to determine the output laser
beam size. An alignment shutter (not shown) may also be used as an
adjustable beam block. Through the wall adjusters ("TWAs") may be
used to enable an operator to adjust the internal imaging relay
mirror mounts for a respective individual mirror (not shown), e.g.,
contained in the mirror mounts, e.g., 98A or 98B, and/or the
alignment shutter from outside an OPuS enclosure without breaking
the seal of the enclosure. An insertable prism may be inserted into
the beam path using through the wall adjusters in order to, e.g.,
direct the beam out through an alignment port, e.g., to measure
beam energy with a power meter head can be attached, e.g., for
alignment purposes.
[0036] According to aspects of an embodiment of the disclosed
subject matter certain interfaces may be used including the
following. The output beam from the BAM 60 may be directed to the
OPuS module 62, and the output beam from the OPuS module 62 may be
directed to the autoshutter 64, with, e.g., beam line tubes (not
shown) providing a purged environment for the optical transfer
between the three modules. The beam may be temporarily redirected
to an alignment port (not shown) which may be used for calibrating
the BAM 60 power meter. The OPuS module 62 may be attached and
mounted vertically to an optical table (not shown) within the laser
10 frame enclosure, which optical table may also have attached to
it the output coupler 34, line narrowing module 32, MO and PRA WEBs
38, 52 and beam reverser 54. The OPuS module 62 may be positioned
between the BAM 60 and the autoshutter 64. The beam line tubes,
which provide the optical interface between the OPuS module 62, BAM
60, and the autoshutter 64, may also mechanically interconnect the
three modules. The alignment port may have a flange that interfaces
with a power meter head. The OPuS module 62 may need to be purged,
e.g., with dry nitrogen to reduce the oxygen and water content of
the gas within the OPuS module 62. The MO WEB 38, PRA WEB 52, BAM
60, autoshutter 64, and OPUS module 62 may be housed together in
one continuous volume, with, therefore, no need for beam lines in
between the modules as might be the case for separate one or more
of such modules.
[0037] The design of the OPUS module 62 may assume certain values
for certain characteristics of the input beam and/or the physical
size and location of neighboring modules. Table II below lists some
exemplary values for such parameteres.
TABLE-US-00002 TABLE II Parameter Design Assumption Input Pulse
T.sub.IS <40 nsec, and preferably .gtoreq.35 <40 (although
longer pulses will produce greater output pulse lengths, the fixed
delay of the OPuS can cause the magnification factor of the OPuS to
decrease for pulse lengths >22 nsec) Incoming Pulse Energy 25 mJ
maximum 18 mJ nominal Wavelength 193.25-193.45 nm Repetition Rate
1-6000 Hz Incoming Horizontal 15.0 mm Beam Size Incoming Vertical
Beam 15.0 mm Size Static Input Pointing .+-.1 mrad max, using the
center of FW10% Variation Static Input Beam .+-.0.2 mm Position
Variation Spatial Coherence Horizontal < 50% Contrast (pin hole
separation 300 micron, 8xReduction) Vertical < 50% Contrast (pin
hole separation 200 micron)
[0038] According to aspects of an embodiment of the disclosed
subject matter, certain parameters may be used, e.g., to identify
performance requirements of an OPuS module 62. Testing against
these performance requirements can be used to validate the module
design. It should be noted that most of the performance
requirements have been defined in terms of upper limits to the
added contribution from the module 62 to the particular beam
parameter, which may, e.g., be monitored under laser-operating
conditions.
[0039] The below Table III may be used for OPuS Specifications.
TABLE-US-00003 TABLE III Parameter Specification TIS Pulse Length
XLR OPuS > 4 Magnification (for input pulse lengths less than 40
nsec) Lifetime >20 .times. 10.sup.9 pulses Pointing Stability
<25 .mu.rad Measured at FW10% Module Dimensions ~1750 .times.
125 .times. 250 mm Leak Rate 5 .times. 10.sup.-5 sccs with a
maximum pressure difference of 25 kPa Beam Size 12.0 .times. 12.0
.+-. 0.05 mm Measured at FW5%. Horizontal <25 .mu.rad Divergence
Measured at FW10% Vertical Divergence <25 .mu.rad Measured at
FW10% Horizontal Beam .ltoreq.5% Symmetry Measured at FW5% Vertical
Beam .ltoreq.5% Symmetry Measured at FW5%
[0040] At least one of the imaging relay mirrors in each optical
tower, e.g., e.g., 154, 158, 162, 168, 172, 176 and 180 of the
first delay path 150 or 194, 195, 198 and 202 in the second delay
path 190, may have orthogonal tilt adjustment accessible from
outside the enclosure. For example, a 4.times. OPuS 62, such as
described in the present application by way of example, may have
eight tilt adjustments, which may be made accessible by through the
wall adjusters. The TWA's can enable an operator to adjust the
imaging relay mirrors or some of them, e.g., along with the
Alignment Shutter without breaking the sealed nitrogen purged
volume. Such adjustments may be used, e.g., in conjunction with a
beam analysis tool, e.g., connected to a metrology access port of,
e.g., the autoshutter. Additionally, the remaining imaging relay
mirrors may have tilt adjustments accessible from only from inside
the enclosure, e.g., for positioning during manufacturing or field
service requiring the breaking of the purge containment, e.g., in
the enclosure housing the delay path towers. The purpose of these
adjustments may be, e.g., to compensate for tolerance build up of
the positioning of the respective imaging relay mirror or
mirrors.
[0041] The OPuS module 62 may, e.g., be capable of producing a
T.sub.IS magnification of >2. for input pulse lengths of, e.g.,
less than 40 ns T.sub.IS. The module 62 may have a first 42 nsec
delay path 150 and a second 18 nsec delay. The magnification
achieved will be a function of delay lengths and the beamsplitter
reflectivities. The design of a dielectric beam splitter may
include, e.g., a partial reflective coating on one side and an
anti-reflection coating on the other. Both coatings may be designed
for an angle of incidence of 45 degrees and an S polarization
orientation. To reduce the effects of power induced birefringence,
the coating material may be chosen to minimize absorption. The beam
splitter substrate may also need to be made from a material to
mitigate absorption and any lifetime concerns. A birefringence null
orientation may be identified and marked on the part according to
co-called "clock" the part, i.e., install it with the proper
orientation.
[0042] The following Table III may be used for beam splitter
specifications.
TABLE-US-00004 TABLE III OPuS Dielectric Beam Splitter
Specifications Parameter Specification Wedge Angle <1 Arc Minute
Transmitted Wavefront <.lamda./10 peak to valley @ 633 nm
Reflective Coating 60% .+-. 3% for 45 degree AOI and S polarization
Anti-Reflective Coating The sum of the reflection from the
reflective coated side and the total transmission of the optic
>98%
[0043] An output energy of 15.0 mJ, a beam size of 12.times.12 mm,
a throughput efficiency of 72% (4.times. OPuS), and a
multiplication factor due to multiple round trips of 1.5, leads to
a maximum expected energy density for each mirror of about 13.6
mJ/cm.sup.2. The following Table V may be used for imaging relay
mirror specifications.
TABLE-US-00005 TABLE V OPuS IRM Specifications Parameter
Specification Radius of Curvature 1660 .+-. 1.66 mm 1350 .+-. 1.35
mm Concentricity <0.05 mm Reflected Wavefront <.lamda./5 Peak
to Valley @ 633 nm Reflective Coating >97% at 0 degrees AOI
[0044] A beam tube may be used to protect the beam entering the
OPuS module 62 from the BAM 60. Similarly, a beam tube may be
needed to seal the beam as it is outputted to the AS module 64.
These beam tubes may form a mechanical interface to the other
optical modules, e.g., using bellows seals. The seals between the
beam tube and the module should be of vacuum quality, and proven
not to out gas or deteriorate in a DUV environment. The OPuS module
62 may require purging, e.g., nitrogen (N.sub.2) purging. A single
purge gas input line may be divided into three lines by a manifold
attached to the OPuS 64 enclosure as shown in more detail in the
above referenced Ser. No. 11/805,583 co-pending patent application.
There will also be two exhaust ports tubing.
[0045] Turning now to FIGS. 6-10D there is shown a PRA WEB assembly
300 according to aspects of an embodiment of the disclosed subject
matter. An example of a PRA WEB assembly 300, referring to FIG. 6,
is shown illustratively to include a PRA WEB assembly box bottom
301, shown in more detail with its contents in FIGS. 8A-C, and a
PRA WEB assembly box top 302, shown in more detail along with its
contents in FIGS. 7A-D. As seen in FIGS. 8A, 8B and 8C the PRA WEB
assembly 300 enclosure box bottom 301 may contain a turning mirror
bracket assembly 304 upon which may be mounted a MO WEB turning
mirror 305, a PRA WEB optics assembly 306 and an optics assembly
position actuator assembly 307. The target position actuator
assembly 307 may further include a target assembly position
actuator translator carrier assembly 308. The PRA WEB optics
assembly 306 is described in more detail in connection with FIGS.
10A, 10B and 10C.
[0046] The PRA WEB turning mirror bracket assembly 304 may include,
e.g., a through the wall adjuster ("TWA") 322, which may include a
pair of through-the-wall adjuster hexagonal plungers 342 and a pair
of stainless steel wire compression springs 336, cooperating with a
respective one of a pair of adjustment screws 317, each connected
to an external adjustment bushing 343 and gasket 333, which
plungers 342 may be held in place against the spring action of
springs 336 by a neck on a respective adjuster assembly 322. The
adjusters 322 may be held in place to the respective adjustment
screw 317 by a respective stainless steel socket head captive screw
354. The plungers 342 may be held in place in a respective turning
mirror adjustment set screw 230 connected to the bracket assembly
304 by a captive screw 232. The bracket assembly 304 may be held in
place in the PRA WEB box bottom 301 by a pair of stainless steel
socket head captive screws 363. The set screws 230 may be connected
to the turning mirror 286 at opposing corners. In operation, as
shown in FIGS. 9B and 9D, the rotation of either of the adjustment
screws 317 can move the turning mirror 305 mount plate 286 to move
the folding mirror 305 in a tilt around pivot ball 234 to tilt the
turning mirror 305 in either or both of two orthogonal axes.
[0047] The PRA WEB assembly box top 302 may also include a cover
purge shield 339 held in place on the ceiling of the box top 302 by
a plurality of stainless steel socket head cap screw 352.
[0048] A stainless steel manual gate valve 309, such as an 11000
series valve such as a QF 40 made by HVA, LLC, of Reno, Nev., e.g.,
with a seal 327, as shown in FIG. 6, may be attached to the outside
of the PRA WEB box bottom 301, e.g., by a pair of gate valve half
clamps 313, attached to the box bottom 301 outer wall by a
plurality of socket cap screws 347.
[0049] FIG. 7D illustrates the through the wall adjustment screw
319 for the MO WEB input alignment target prism position actuator
assembly 309, similar to that shown in FIG. 8B for the adjustment
screw 346 for the target prism adjustment assembly 307 and 345 for
the output coupler horizontal adjustment assembly 400 discussed in
more detail with regard to FIGS. 10A, 10B and 10C, which adjustment
screw 319 may extend through bushing 343 and washer 333, which
bushing 343 may be held in place by a flat brass hex nut 367. As
illustrated, the adjustment screw 319 may be held in the helical AT
341 by a stainless steel dowel pin 350 and the opposing end of the
helical AT 341 may have attached to it an adjustment screw 242,
which may be attached by a stainless steel socket head captive
screw 354. The adjustment screw 242 may be held by a pair or radial
bearings on a cradle 244 mounted on a prism alignment assembly base
plate 236. The adjustment screw 242 may threadingly engage a
traveling block 248 within the cradle 244 and the traveling block
may be attached by stainless steel phillips flat head machined
screw 348 to a prism assembly positioning translator carrier 330,
which may travel on a pair of alignment tool prism positioning
shafts 316. A prism assembly mount 320 may be moved along the
shafts 317 by the translator carrier 330 and may have attached to
it a prism mounting bracket 250, to which may be attached an
alignment prism such as a 25 mm, UV grade fused silica right
triangle prism 325, by a pair of stainless steel socket head
shoulder screws 368 and optical mirror mounting clips 349 attached
to the prism mount 250 by stainless steel socket head captive
screws 351. The alignment shafts 316 may extend from an interface
assembly mount 321, which may be attached to the bracket 310 by
stainless steel socket head captive screws 363, which screws 363
may also be used to attach face plates 252 to the cradle 244 and to
attach the prism guide bracket 310 and the translator adjustment
screw cradle base plate 236 to the ceiling of the PRA WEB assembly
box top 302. Stainless steel precision ground balls 331 mounted in
recesses in the prism assembly mount 320 may serve to seat in a
repeatableprism assembly "alignment" position.
[0050] As shown by way of example in FIG. 8B a target prism
position actuator assembly 307 may include, e.g., a base plate 236
and a cradle 245 attached to the base plate 236. A helical AT 240,
similar to that shown in more detail as 341 in FIG. 7D, along with
an adjustment screw 346 which extends through the wall through a
bushing 343 and washer 333 shown in FIG. 8B and similar to that
shown in more detail in FIG. 7D. A PRA WEB target assembly mounting
bracket 254 may abut the optics assembly 306 when in position and
may also be connected to target assembly positioning actuator
assembly 307 by a dowel pin 256, for movement with the actuator
assembly 307. The cradle 245 may have an associated face plates 253
and the adjustment screw 243 contained in the cradle 245 by radial
bearings for rotational motion to move a traveling block 249 to
which may be attached the actuator assembly 308.
[0051] As shown in more detail in the exploded view of FIGS. 10B
and 10C by way of example, the target mounting block 254 may travel
on a pair of PRA WEB target travel alignment shafts 411, which may
be attached to the optic mounting block 306 by a precision land
conic foot 408 on the one hand and a precision land foot slotted
foot 409 on the other hand, and connected by a respective one of a
pair of stainless steel socket head captive screws 431. A brass
adjustment screw nut 424 threaded on the respective screw 431 may
hold a respective magnet 427 inside a sleeve formed by the
respective foot 408, 409. The respective magnets may serve to
minize any error in the force applied to seat the prism assembly to
its "alignment" position.
[0052] The target alignment prism mount assembly mounting block 254
may be limited in travel along the rods 411 by travel stop notches
264, which may be used to adjust the alignment target prism 258
when in place and which may be adjusted in position by the use of
the screws 431 and the feet 408 and 409.
[0053] The optical mount 306 may be attached to the floor of the
PRA WEB assembly box bottom 301 by stainless steel screws 270,
similar to screws 363, two of which may be used in association with
a respective one of a pair of flexured mountings 490, 492. The
flexured mounts may each have a straight groove 486 and a multiple
leg groove 486 which form between them a thin flexure arm 485
giving the optic mount flexibility to move with respect to the
screw 270 in a direction perpendicular to the longitudinal axis of
the thin arm 485, while being relatively more stiff in the
orthogonal axis, e.g., to account for differential thermal
expansion of the box bottom 301 and the optic mount 306.
[0054] A Zr--Cu PRA WEB optics assembly mount 401 may include,
e.g., a beam expansion optics prism assembly mount 404, which
mounting plate 404 may be attached to the optics mount 306 in a
suitably sized and shaped alcove by a plurality of stainless steel
screws 270 similar to screws 363, at least two of which may be
utilized in association with a respective one of a pair of flexured
mounts 480, 482. The flexured mount 480 may be formed by a pair of
straight slots 486 through the mounting plate 404 and a plurality
of surrounding slots 484 forming between then two pairs of flexured
arms 485 which give the mounting plate some flexibility of movement
in a direction perpendicular to the flexured arms 485. The flexured
mount 482.may, e.g., include a straight slot 486 similar to as is
illustrated for flexured mounting 480 and a multilegged slot 488,
shown in more detail in FIGS. 9a and 10A, which together with the
straight slot 484 and the rest of the mounting plate 404 form two
generally orthogonal flexure arms 485a, 485b, giving the mounting
plate 404 some flexibility of movement both perpendicular to the
first flexure arm 485a and to the second flexure arm 485b relative
to the respective stainless steel socket head captive mounting
screws 435.
[0055] Mounted to the beam expanding optics mounting plate 404, as
shown, e.g., in FIGS. 10A, 10B and 10C may be a first beam expander
prism first half 470, a second beam expander prism 472, and a first
beam expander prism second half 474, each attached to the mounting
plate 404 by a respective first beam expander prism first half
mounting member 476, a second beam expander prism mounting member
478, and a first beam expander prism second half mounting member
480, each of which may be glued to the mounting plate 404 and the
respective beam expanding prism 470, 472 and 474. The operation of
the beam expander prisms is explained in more detail in the above
referenced co-pending Ser. No. 11/787,180 application. The
respective prisms 472, 474 may be held in place and aligned with
each other also, e.g., by brackets scatter shields 405, 406 which
may be attached to the mounting plate 404 by stainless steel socket
head captive screws 436.
[0056] An output coupler horizontal adjustment assembly 400, shown,
e.g., in FIGS. 10A and 10B, may serve to rotate the output coupler
mount 419 around a horizontal axis, denominated a horizontal axis
vis a vis the illustration in FIGS. 10A, 10B and 10C, for
convenience of disclosure and by way of example only and need not
be aligned with horizontal in use, which mount 419 may contain a
Zr--Cu PRA WEB output coupler mount 419 in an output coupler
opening 443. A PRA WEB light shield 449 may be mounted on the
mounting plate 404 by a pair of stainless steel socket head captive
screws 453. The output coupler horizontal adjustment assembly 400
may include a Zr--Cu PRA WEB horizontal mount assembly front plate
413, which may be attached to the optic mount 306 by a plurality of
stainless steel socket head captive screws 428. A stainless steel
single ended flexural pivot upper bearing 414, such as a C-Flex
bearing made by Bearing Co. Inc., of Frankfort N.Y., may attach a
Zr--Cu PRA WEB horizontal adjust lever assembly 415 to the front
plate 413 for rotation on the bearing 414 about a vertical axis and
with respect to the stationary front plate 413. The bearing 414 may
be held in place by a stainless steel socket head cap screw 429
tightening an upper clamp 274 on the lever portion 415 and may be
held in place with respect to the front plate 413 by a stainless
steel socket head cap screw 429 tightening an upper clamp 276 on
the front plate 413. A lower stainless steel single ended flexural
pivot bearing 414 may hold the lever assembly 415 for rotation
about a vertical axis with respect to the bearing and the front
plate 413. The upper bearing 414 may be held in place with respect
to the lever assembly 415 by a for rotation about the bearing 414
with respect to the front plate 413 and held in place by a
stainless steel socket head cap screw 429 tightening a lower clamp
274 on the lever portion 415 and may be held in place with respect
to the front plate 413 by a stainless steel socket head cap screw
429 tightening a lower clamp 276 on the front plate 413. In an
opening between the clamps 274 may be formed a ridge 278 with a
truncated triangular extension 280, which may engage a similar
triangular groove 282 on the output coupler mount 419 and hold in
compression between the ridge 278 and the groove 282 a precision
ground stainless steel pivot ball (not shown).
[0057] The through the wall adjuster screw 345 may be held in place
on an adjuster 322 by a screw 354. A hexagonal plunger 342 may
engage a hexagonal female opening in a set screw 422, such that
rotation of the through the wall adjuster screw 345 rotates the set
screw 422 and the set screw ball end moves the lever assembly 415
against the spring pressure of spring 430 between the front plate
413 and lever assembly 415. This pivots the end of the lever
assembly 415 around the bearings 414 to apply force in a generally
horizontal plane to the output coupler mount 419 through the ball
(not shown) interacting with the mount 419 in the groove 282
[0058] The output coupler horizontal adjustment assembly may
include, e.g., a through the wall actuator assembly shown, e.g., in
FIG. 7a within the PRA WEB assembly box top 302 and having an
adjustment screw 317 extending through the ceiling of the PRA WEB
assembly box top 302 into a bushing 343 and washer 333, with a
locking nut 367 internal to the box top 302. As with the other
illustrated through the wall adjustment screws, e.g., 319, 345, 346
the adjustment screw is associated with a through the wall adjuster
322, housing a plunger 342 and a compression spring 336 and is held
in place on the adjustment screw 317 by a screw 354. The plunger
342 may engage a set screw 422 passing through a brass set screw
adjustment nut 425 in an output coupler vertical adjustment
assembly 500, to engage a vertical adjust recess in a vertical
adjust lever 417. The vertical adjust lever 417 may be held for
rotational movement about a flex bearing 414 held in clamps on the
vertical adjust assembly 500 by stainless steel socket head cap
screw 433. Rotation of the lever 417 about the bearing 414 applies
force to the output coupler mount 419 against the spring pressure
of springs 430 connected between the output coupler mount 419 and
the optics assembly 306, to rotate the output coupler mount 419
about the pivot ball (not shown) engaging the slot 282 on the
output coupler mount 419 around a horizontal axis.
[0059] The output coupler may be held in the output coupler opening
443 in the mount 419 by an plurality of optic spring clips 420 on
an optic spring clip ring 272 opposing a plurality of output
coupler 442 optic holding members 473 on the mount 419 and
extending into the opening 443. A plurality of springs 430, e.g.,
three springs 430 may be held in place on the output coupler mount
419 by one of a respective plurality of stainless steel flat point
socket hex set screws 441, two of which may be held in place
relative to the mounting plate by a respective one of a pair of
stainless steel socket shoulder screws 423 and one of which may be
held in place in relation to the optic mount by a stainless steel
flat point socket hex set screws 440. The output coupler 442 may be
a CaF.sub.2 193 nm 20% reflective 45.degree. clocked output coupler
442.
[0060] The output coupler vertical adjust assembly 500 may be
attached to the optical assembly 306 by an attachment assembly 296,
which may consist of, e.g., a stainless steel shoulder socket screw
454 a flat washer 456 and a stainless steel wire compression spring
455. A Zr--Cu PRA WEB vertical adjust guide 418 may be attached to
the vertical adjust assembly 500 by a pair of screws 432. A spring
430 may be connected to the vertical adjust assembly 500 by a pin
inserted in dowel pin hole 294 and to the lever assembly 417 by a
dowel pin inserted into dowel pin hole 298.
[0061] An R.sub.MAX mirror 443, e.g., highly reflective p polarized
CaF.sub.2 45.degree. R.sub.MAX mirror 443 may be held in place in
an R.sub.MAX opening by a spring clip 444, which may be attached to
the optics assembly 306 by a plurality of stainless steel socket
head cap screws 439 and stainless steel split lock washers 438. A
heat sink (not shown) may be attached to a heat sink mounting
member 379, e.g., as shown in FIG. 8C to be attachable to the floor
of the box bottom 301 by a plurality (only one shown) of screws
363. The heat sink mount 379 may also have attached to it a light
shield 378 by a plurality of screws 363.
[0062] As seen by way of example in FIG. 6. an alignment window
interlock assembly 290, for the alignment opening 220, may include,
e.g., a 30 mm round.times.4 mm thick CaF.sub.2 window 323 and an
external pressure c-seal 326 and a foil ring 329 held in place in
the opening 220 by a window clamp 315 and socket head captive
screws 357. A window clamp 340 with a cover flange may be held in
place over the window clamp 315 by steel socket head captive screws
359 and a centering ring assembly 335 and a clocked cover 334 may
be held in place on an annular flange on the flanged mount assembly
340 by a clocked assembly clamp 338, with a pin dowel pin 282
aligning the clamp 338 to the clocked grooves on the clamp 340 and
the cover 334 such that the interlock paddle 311, which inserted
into an interlock paddle slot 284 on the cover assembly clamp 338,
and held in place there by screws 354, will engage a limit switch
actuator on a LAM interlock assembly 312 held on the outside of the
PRA WEB assembly box top 302 by stainless steel socket head captive
screws 376 and associated washers 377.
[0063] Also seen in FIG. 6 is another alignment window assembly
with a window clamp 315, without a cover plate or interlock, for
the opening 221 for aligning the output coupler 442 and an exploded
view of another window assembly, without a cover plate or interlock
for the opening 226, used with the alignment target prism 258.
Knobs 374, with internal fittings (not shown) to interface with a
respective through the wall adjustment screw 317, 319, 345, 346 may
be used for adjustment rotation of the respective adjustment screw
317, 319, 345, 346. Bellows assemblies (not shown) may connect the
PRA WEB assembly 300 to the amplifier section of the laser system,
the power ring amplifier ("PRA") chamber 50 at the gate valve 309,
and to the PRA WEB output to the BAM 60 through opening 224 and the
PRA WEB 300 input from the oscillator section 12 of the laser
system 10, through opening 210.
[0064] It will be understood by those skilled in the art that,
according to aspects of an embodiment of the disclosed subject
matter, an apparatus and method are disclosed which may comprise a
pulsed gas discharge laser lithography light source, among other
purposes, such as an excimer laser such as an ArF, KrF laser or an
F.sub.2 molecular laser, which may comprise a seed laser portion,
e.g., a master oscillator, providing a seed laser output light beam
of seed pulses; an amplifier portion, such as a ring power
amplifier, as discussed in the above referenced co-pending Ser. No.
11/787,180 patent application, receiving the seed laser output
light beam and amplifying the optical intensity of each seed pulse
to provide a high power laser system output light beam of output
pulses, e.g., at ninety or more Watts and at or above 4 kHz,
preferably at or about 6 kHz, e.g., as may be necessary and
required for current and future generations of immersion
lithography while maintaining the economics of non-immersion state
of the art lithography processes, e.g., with respect to throughput,
beam quality parameters, dose and dose stability and the like
requirements; a pulse stretcher increasing the number of peaks in
the output pulse and decreasing the average peak intensity of each
of the output pulses by passing the output pulses through a pair of
optical delay paths in series; the pulse stretcher may comprise: a
first beam splitter operatively connected with the first delay path
and a second pulse stretcher operatively connected with the second
delay path; a first optical delay path tower containing the first
beam splitter, e.g. made up of a pair of mirror mounts holding,
e.g., imaging relay mirrors for the first delay path in an
enclosure with the first beam splitter including a beam splitter
enclosure box and two end boxes; a second optical delay path tower
containing the second beam splitter, e.g., also within the
enclosure and, e.g., in the box housing the first beam splitter
and, e.g., also a pair of mirror mounts holding, e.g., imaging
relay mirrors and contained in the respective end boxes; one of the
first and second optical delay paths may comprise: a plurality of
mirrors defining the respective optical delay path including
mirrors located in the first tower and in the second tower; the
other of the first and second optical delay paths may comprise: a
plurality of mirrors defining the respective optical delay path
including mirrors only in one of the first tower and the second
tower. The first optical delay path and the second optical delay
path may be of unequal length. The first optical delay path may be
longer than the second optical delay path. The other of the first
and second optical delay towers containing mirrors in both of the
first and second towers may be the longer of the first and second
optical delay paths. The longer of the first and second optical
delay paths may be the first optical delay path in the series
arrangement. The mirrors may comprise imaging mirrors and/or
confocal mirrors.
[0065] Those skilled in the art will understand that, according to
aspects of an embodiment of the disclosed subject matter, an
apparatus and method are disclosed which may comprise a pulsed gas
discharge laser lithography light source, such as noted above, for
immersion lithography uses, among other purposes, which may
comprise a seed laser portion providing a seed laser output light
beam of seed pulses; an amplifier portion, e.g., as noted above,
receiving the seed laser output light beam and amplifying the
optical intensity of each seed pulse to provide a high power laser
system output light beam of output pulses, such as is discussed
above; the amplifier portion may comprise a ring power amplifier
which may comprise amplifier portion injection optics which may
comprise at least one beam expanding prism, a beam reverser and an
input/output coupler; the beam expansion optics and the output
coupler may be mounted on an optics assembly with the beam
expansion optics rigidly mounted with respect to the optics
assembly and the input/output coupler mounted for relative movement
with respect to the optics assembly for optical alignment purposes.
The input/output coupler may be mounted for movement with respect
to the optic assembly in a first axis and a second axis. The first
axis and second axis may be generally orthogonal to each other. The
amplifier injection optics may be contained within an amplifier
portion injection optics assembly box and the input/output coupler
may comprise at least one through-the-wall adjusting actuator to
adjust the position of the input/output coupler in at least one
axis.
[0066] It will be understood by those skilled in the art that the
aspects of embodiments of the disclosed subject matter are intended
to be possible embodiments or portions of possible embodiments only
and not to limit the disclosure of the disclosed subject matter in
any way and particularly not to a specific possible embodiment or
portion of a possible embodiment alone. Many changes and
modification can be made to the disclosed aspects of embodiments of
the disclosed subject matter that will be understood and
appreciated by those skilled in the art. The appended claims are
intended in scope and meaning to cover not only the disclosed
aspects of embodiments of the disclosed subject matter but also
such equivalents and other modifications and changes that would be
or become apparent to those skilled in the art. In addition to
changes and modifications to the disclosed and claimed aspects of
embodiments of the disclosed subject matter others could be
implemented.
[0067] While the particular aspects of the embodiment(s) of the
IMMERSION LITHOGRAPHY LASER LIGHT SOURCE WITH PULSE STRETCHER
described and illustrated in this patent application in the detail
required to satisfy 35 U.S.C. .sctn.112 are fully capable of
attaining any above-described purposes for, problems to be solved
by, or any other reasons for or objects of the aspects of an
embodiment(s) above described, it is to be understood by those
skilled in the art that presently described aspects of the
described embodiment(s) of the disclosed subject matter are merely
exemplary, illustrative and representative of the subject matter
which is broadly contemplated by the disclosed subject matter. The
scope of the presently described and claimed aspects of embodiments
or portions of embodiments fully encompasses other embodiments or
portions of embodiments which may now be or may become obvious to
those skilled in the art based on the teachings of the
Specification. The scope of the present IMMERSION LITHOGRAPHY LASER
LIGHT SOURCE WITH PULSE STRETCHER is solely and completely limited
by only the appended claims and nothing beyond the recitations of
the appended claims. Reference to an element in any such claim in
the singular is not intended to mean nor shall it mean in
interpreting such claim element "one and only one" unless
explicitly so stated, but rather "one or more". All structural and
functional equivalents to any of the elements of the
above-described aspects of an embodiment(s) that are known or later
come to be known to those of ordinary skill in the art are
expressly incorporated herein by reference and are intended to be
encompassed by the present claims. Any term used in the
Specification and/or in the claims and expressly given a meaning in
the Specification and/or claims in the present application shall
have that meaning, regardless of any dictionary or other commonly
used meaning for such a term. It is not intended or necessary for a
device or method discussed in the Specification as any aspect of an
embodiment or portion of an embodiment to address each and every
problem sought to be solved by the aspects of embodiments or
portions of embodiments disclosed in this application, for it to be
encompassed by the present claims. No element, component, or method
step in the present disclosure is intended to be dedicated to the
public regardless of whether the element, component, or method step
is explicitly recited in the claims. No claim element in the
appended claims is to be construed under the provisions of 35
U.S.C. .sctn.112, sixth paragraph, unless the element is expressly
recited using the phrase "means for" or, in the case of a method
claim, the element is recited as a "step" instead of an "act".
[0068] It will be understood also be those skilled in the art that,
in fulfillment of the patent statutes of the United States,
Applicant(s) has disclosed at least one enabling and working
embodiment of each invention recited in any respective claim
appended to the Specification in the present application and
perhaps in some cases only one. For purposes of cutting down on
patent application length and drafting time and making the present
patent application more readable to the inventor(s) and others,
Applicant(s) has used from time to time or throughout the present
application definitive verbs (e.g., "is", "are", "does", "has",
"includes" or the like) and/or other definitive verbs (e.g.,
"produces," "causes" "samples," "reads," "signals" or the like)
and/or gerunds (e.g., "producing," "causing", "using," "taking,"
"keeping," "making," "sampling," "determining," "measuring,"
"calculating," "reading," "signaling," or the like), in defining an
aspect/feature/element of, a step of, an action of or functionality
of, and/or describing any other definition of an
aspect/feature/element of or step of or action/functionality of, an
embodiment or portion of an embodiment of a method or apparatus
which is within the subject matter being disclosed. Wherever any
such definitive word or phrase or the like is used to describe an
aspect/feature/element of or step of or action or functionality of
or the like of any of the one or more embodiments or portions of
embodiments disclosed herein, e.g., any feature, element, system,
sub-system, component, sub-component, process or algorithm step,
particular material, or the like, it should be read, for purposes
of interpreting the scope of the claimed subject matter of what
applicant(s) has invented, and claimed in the appended claims, to
be preceded by one or more, or all, of the following limiting
phrases, "by way of example," "for example," "as an example,"
"illustratively only," "by way of illustration only," etc., and/or
to include any one or more, or all, of the phrases "may be," "can
be", "might be," "could be" and the like. All such aspects,
features, elements, steps, materials, actions, functions and the
like should be considered to be described only as a possible aspect
of the one or more disclosed embodiments or portions of embodiments
and not as the sole possible implementation of any one or more
aspects/features/elements of or steps of or actions/functionalities
of, or the like of, any embodiments or portions of embodiments
and/or the sole possible embodiment of the subject matter of what
is claimed, even if, in fulfillment of the requirements of the
patent statutes, Applicant(s) has disclosed only a single enabling
example of any such aspect/feature/element of or step of or action
or functionality of, or the like of, an embodiment or portion of an
embodiment of the subject matter of what is claimed. Unless
expressly and specifically so stated in the present application or
the prosecution of this application, that Applicant(s) believes
that a particular aspect/feature/element or step of or action or
functionality of, or the like of, any disclosed embodiment or any
particular disclosed portion of an embodiment of the subject matter
of what is claimed, amounts to the one an only way to implement the
subject matter of what is claimed or any aspect/feature/element or
step of or action/functionality or the like of the subject matter
disclosed and recited in any such claim, Applicant(s) does not
intend that any description of any disclosed aspect/feature/element
or step of or action or functionality or the like of, any disclosed
embodiment or portion of an embodiment of the subject matter of
what is disclosed and claimed in the present patent application or
the entire embodiment shall be interpreted to be such one and only
way to implement the subject matter of what is disclosed and
claimed or any aspect/feature/element or step of or action or
functionality of or the like of such subject matter, and to thus
limit any claim which is broad enough to cover any such disclosed
implementation along with other possible implementations of the
subject matter of what is claimed, to such disclosed
aspect/feature/element or step of or action/functionality of or the
like of such disclosed embodiment or any portion of such embodiment
or to the entirety of such disclosed embodiment. Applicant(s)
specifically, expressly and unequivocally intends that any claim
that has depending from it a dependent claim with any further
detail of any aspect/feature/element, step, action, functionality
or the like of the subject matter of what is recited in the parent
claim or claims from which it directly or indirectly depends, shall
be interpreted to mean that the recitation in the parent claim(s)
was broad enough to cover the further detail in the dependent claim
along with other possible implementations and that the further
detail was not the only way to implement the aspect/feature/element
claimed in any such parent claim(s), and thus that the parent claim
be limited to the further detail of any such
aspect/feature/element, or step, or action/functionality, or the
like, recited in any such dependent claim to in any way limit the
scope of the broader aspect/feature/element or step or
action/functionality or the like of any such parent claim,
including by incorporating the further detail of the dependent
claim into the parent claim.
* * * * *